Temperatures dropped to minus 0.8 degC in Oamaru, minus 4.5 degC in Alexandra, minus 5.5 degC at Dunedin airport and minus 2 degC in Wanaka.
MetService meteorologist Tui McInnes said overnight temperatures in Queenstown dropped to minus 2.1 degC and minus 0.5 degC in Invercargill but they have had colder nights.
He said the coldest temperature for the Otago and Southland regions was minus 5.5 degC recorded at Dunedin airport but there would have been some places colder where there were no weather stations.
A cool start was forecast for this morning with more frosts, but not as cold as yesterday, Mr McInnes said.